This invention relates to thin film solar cells and more particularly to such solar cells having a layer of nickel on the back contact.
The following U.S. patents are incorporated by reference for all purposes: U.S. Pat. No. 4,517,403 issued May 14, 1985 and U.S. Pat. No. 4,584,427 issued April 22, 1986. These two patents provide a good background of the art of thin film solar cells and efforts made to develop commercially practical devices. For example, U.S. Pat. No. 4,517,403 illustrates commercially practical series interconnection of thin film solar cells and U.S. Pat. No. 4,584,427 provides an improvement which reduces internal resistance in individual cells. Commercially practical solar modules have been manufactured according to the teachings of these two patents. In the commercial devices, the stitch bars used to interconnect adjacent cells were formed by screen printing a paste including silver. The back contacts of cells were formed from sputtered aluminum. When this structure was scaled up to a large module, for example one foot wide by four feet long, a problem was encountered. When such large modules were tested according to Jet Propulsion Laboratory Block V test procedure, a significant reduction in module fill factor was experienced. As a result, it was apparent that some improvement to the method of manufacture or structure of the devices was needed to avoid this reduction of fill factor.